1. Field of the Invention
This invention relates to an apparatus and process for conveyance of solids by a screw conveyor operated in an inclined position to deliver solids which are relatively free of surface liquids. Solids are frequently transferred between zones of substantially different pressures wherein the solid materials are supplied to a liquid containing lockhopper and the solid materials with associated liquid are introduced to an inclined screw conveyor for passage to a vessel such as a pressurized reaction vessel. The liquid in the lockhopper acts as a liquid seal between the pressurized reaction vessel and the lockhopper feed supply which is at a much lower pressure. Utilization of the solids dewatering screw conveyor according to the present invention provides solid materials substantially free of liquids being passed to a vessel, such as a pressurized reaction vessel after being passed through a liquid sealed lockhopper.
2. Description of the Prior Art
The prior art has recognized the need for an improved apparatus and process for conveyance of solids from a zone wherein the solids are contained in a liquid to a zone wherein the solids are desirably substantially free of the liquid, the solids and liquid being separated within the conveyance system. This is especially true for coal or oil shale reactor applications where the solids are most desirably as dry as possible. The problems in solids separation from liquids during solids conveyance increase when continuous high speed conveyance is desired.
One means of conveying and separating solid particles from a liquid is by drag bar conveyors or forked tine systems such as exemplified by U.S. Pat. No. 4,322,184. Similarly, perforated buckets mounted on an endless belt have been used for conveying and separating solid materials from liquids, such as taught by U.S. Pat. No. 4,401,402. However, these systems do not provide desired solids-liquid separation, especially at high speed conveyance.
Feeding of solids from a liquid sealed solids lockhopper to a pressurized reactor by screw conveyors is well known as exemplified by U.S. Pat. No. 3,729,105. The recognition of undesired liquid carryover into a pressurized reactor and the need for further solids/liquid separation and one solution has been taught by U.S. Pat. No. 4,247,240 wherein solid materials are transferred from a liquid filled lockhopper by a conveying screw to a solids/liquid separator chamber wherein solids are passed over a screen separator permitting the liquid to fall to a reservoir at the bottom and the solids pass substantially liquid-free into the pressurized reactor. There have been several attempts to improve solids/liquid separation during transport by screw conveyors. One such attempt of improved solids separation from liquids in the screw conveyor itself is taught by U.S. Pat. No. 4,270,447 teaching an upwardly inclined helical screw with decreasing diameter towards its upper portions to "squeeze" out much of the water from very fine particulates, such as coal dust and cement. In another approach, U.S. Pat. No. 3,062,129 teaches a helical screw conveyor which revolves within a perforated cylinder and squeezes the solids to extract the liquid sideways through a perforated inner housing to drain downwardly. Various screw conveyor systems providing liquid removal through wall screens are taught by U.S. Pat. Nos. No. 3,950,146, 3,950,147, and 4,017,270. Drag bar conveyors are also known with wall screens to provide liquid removal through the screened openings. Such systems present problems with screen clogging by fines and with larger solids jamming in screen slots and scoring the housing or fracturing the screens.
Seeking to avoid these disadvantages in the separation of solids from liquids in an inclined helical screw conveyor, it has been proposed to provide the flights of a helical conveyor with cutout portions adjacent the shaft to separate liquid from particulate material and allow passage of the liquid downwardly along the inclined conveyor system as shown in U.S. Pat. No. 4,297,208. The U.S. Pat. No. 4,297,208 recognizes that when in operation the surface of the solids being conveyed lie at an angle to the horizontal and toward the upcoming side of the screw as shown in FIG. 4 of that patent. The U.S. Pat. No. 4,297,208 teaches the corner of the housing beneath the upcoming side of the screw conveyor is spaced a greater distance from the flight to allow higher efficiency in draining the liquid from the particulate material.